This invention relates to a capacitive sensing device and more particularly to a device used to sense the presence of conducting and nonconducting objects in the vicinity of the path of a camera optical probe during its movement about a terrain model board of a simulator complex such as is used in pilot training.
Visual display systems used with aircraft simulation and comprising a closed-circuit television system in which a television camera is moved about a three-dimensional terrain model have gained widespread use in the field of aircraft simulation. Apparatus and techniques for controlling camera movement as well as transmitting and displaying the image of the terrain model are disclosed in U.S. Pat. Nos. 2,959,779; 3,052,753 and 3,670,426. The three-dimensional model board which is scanned by the TV camera as the camera follows a simulated course of flight determined by the student pilot as the student pilot "flies" the simulation aircraft is fashioned painstakingly with rigorous adherence to correct scale factors so that the trainee can properly judge altitude, altitude rates, slant range, closure rates, etc. The terrain model generally represents a large section of terrain that may include mountains, rivers, buildings, airports, runways, etc., and may have an overall dimension on the order of 20 feet by 40 feet (6.1 by 12.2 meters). The scale of such a terrain model board is so small that a 20 by 40 foot model might easily represent a section of terrain on the order of 6 miles by 12 miles (9.66 by 19.31 kilometers). Because of this large scale factor, it will be appreciated that if a pilot trainee was performing a maneuver that would in real life bring his aircraft within 200 feet (61 meters) of the ground, the television probe or lens would be "flying" about the model board at about 1.6 inches (4.1 centimeters). Similarly, if the pilot were to be performing a maneuver such as landing, that would bring his eyepoint within 20 feet (6 meters) of the ground, the television probe or lens would only be 0.16 (4.1 millimeters) of an inch away from a model board. Thus, it can be seen that as the camera probe moves rapidly along the model board at such close distances, a slight mistake on the part of the trainee pilot or an irregularity in the model board could result in the probe making contact with or crashing into the model board. Such crashing almost always results in damage to either the camera probe or the model board. Therefore, during movement of the optical camera probe over the terrain model board, it is important to sense the presence of nearby objects to prevent the probe, as controlled by the trainee pilot, from crashing into such objects which are not within the field of view of the simulator operator.